xapian-core/backends/multivaluelist.h

   1 /** @file multivaluelist.h
   2  * @brief Class for merging ValueList objects from subdatabases.
   3  */
   4 /* Copyright (C) 2007,2008,2009 Olly Betts
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  19  */
  20
  21 #ifndef XAPIAN_INCLUDED_MULTIVALUELIST_H
  22 #define XAPIAN_INCLUDED_MULTIVALUELIST_H
  23
  24 #include "valuelist.h"
  25
  26 #include "database.h"
  27
  28 #include <string>
  29 #include <vector>
  30
  31 struct SubValueList;
  32
  33 /// Class for merging ValueList objects from subdatabases.
  34 class MultiValueList : public ValueList {
  35     /// Don't allow assignment.
  36     void operator=(const MultiValueList &);
  37
  38     /// Don't allow copying.
  39     MultiValueList(const MultiValueList &);
  40
  41     /// Current docid (or 0 if we haven't started yet).
  42     Xapian::docid current_docid;
  43
  44     /// Vector of sub-valuelists which we use as a heap.
  45     std::vector<SubValueList *> valuelists;
  46
  47     /// The value slot we're iterating over.
  48     Xapian::valueno slot;
  49
  50     size_t multiplier;
  51
  52   public:
  53     /// Constructor.
  54     MultiValueList(const std::vector<Xapian::Internal::intrusive_ptr<Xapian::Database::Internal> > & dbs,
  55                    Xapian::valueno slot_);
  56
  57     /// Destructor.
  58     ~MultiValueList();
  59
  60     /// Return the docid at the current position.
  61     Xapian::docid get_docid() const;
  62
  63     /// Return the value at the current position.
  64     std::string get_value() const;
  65
  66     /// Return the value slot for the current position/this iterator.
  67     Xapian::valueno get_valueno() const;
  68
  69     /// Return true if the current position is past the last entry in this list.
  70     bool at_end() const;
  71
  72     /** Advance the current position to the next document in the value stream.
  73      *
  74      *  The list starts before the first entry in the list, so next()
  75      *  must be called before any methods which need the context of
  76      *  the current position.
  77      */
  78     void next();
  79
  80     /** Skip forward to the specified docid.
  81      *
  82      *  If the specified docid isn't in the list, position ourselves on the
  83      *  first document after it (or at_end() if no greater docids are present).
  84      */
  85     void skip_to(Xapian::docid);
  86
  87     /** Check if the specified docid occurs in this valuestream.
  88      *
  89      *  The caller is required to ensure that the specified @a docid actually
  90      *  exists in the database.
  91      *
  92      *  This method acts like skip_to() if that can be done at little extra
  93      *  cost, in which case it then sets @a valid to true.
  94      *
  95      *  Otherwise it simply checks if a particular docid is present.  If it
  96      *  is, it returns true.  If it isn't, it returns false, and leaves the
  97      *  position unspecified (and hence the result of calling methods which
  98      *  depends on the current position, such as get_docid(), are also
  99      *  unspecified).  In this state, next() will advance to the first matching
 100      *  position after @a docid, and skip_to() will act as it would if the
 101      *  position was the first matching position after @a docid.
 102      *
 103      *  The default implementation calls skip_to().
 104      */
 105     bool check(Xapian::docid did);
 106
 107     /// Return a string description of this object.
 108     std::string get_description() const;
 109 };
 110
 111 #endif // XAPIAN_INCLUDED_MULTIVALUELIST_H